The great Seattle cold-hardy avocado trial

The north winds dislodged some of my fleece blankets and I am sure many of my loquat flowers and fruits were fully exposed. They look ok now but there’s no telling what the damage is.


So disappointing after your prolific flower set! At least you know your loquats are itching to produce fruit.


One plus side of this cold weather, the frost that formed on the inside surface of the greenhouse door is beautiful! I don’t know what this kind of frost formation is called, don’t recall ever having seen anything like this before:


I’ve got the same!

The Vineyard Gazette - Martha's Vineyard News | Frost Feathers.


This weather is so cold that my bedroom window froze and broke!! I’ve never seen anything like this!!

Fortunately there is a second pane of glass to protect the house. But that is freezing too now.

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That’s wild!

The outdoor Jade tree was unprotected other than having wood chips mounded up above the graft, and I’d say based on the degree of cracking and blistering I see on the stems, it’s 100% dead above ground. It’s not super obvious yet, but I think within a week this will look very dead:


It was so cold last night that I suspect loquat and possibly even feijoa fruit next year will be heavily affected. I now even worry about survival of several potted trees.

Based on the last 2 years, I would say my zone is closer to 8A than 9A.


I noticed the feijoa leaves look somewhat curled, probably going to mostly defoliate at least. No signs of frost damage on the loquat yet, but I expect it’ll show delayed signs of damage within a week or two.

Interestingly the guabiju looks solid, just a few leaves damaged. I think it’s a lot more hardy than advertised. No idea if I’ll like the fruit, though.


The freezing at the moment at your side is somewhat exactly the range of tolerance from the hardy avocados. So this will hopefully give some enlightment. We had some similar low temps in eastern germany the last week with three days at -9 °C to -11 °C in unprotected spots.

I hope for all the best and to see some cultivars being the new leads for the project! I and most likely other too are following the crime scene :slight_smile:


I am afraid my outdoor trees are not large enough to handle this kind of long duration freeze, even if maybe some of them could handle a short duration freeze at these same temperatures. If my trees were a few years older, or if the freeze were only for a few hours on one night, then maybe there would be some good data to come from this. But I am expecting extensive losses once I’m able to remove the covers and check things in a few days. I would be shocked if any outdoor trees survive at all, other than the three with heat sources.

As you can see, it has been continuously below -2°C for more than 60 hours already now, and below -4°C for more than 48 hours, and it is not supposed to be above freezing for more than a few moments until Tuesday. The ground has frozen solid to a depth that is likely sufficient to kill the underground portion of the trees already, and is freezing deeper by the minute. As far as I know, even the very hardiest avocados are killed when their roots freeze solid.

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Most of the damage will not be evident yet, but even so it’s pretty clear all exposed avocado tissue is pretty crispy. It’s possible there’s some life in the roots, but with how hard the ground feels, I’m not holding out much hope.

This one got a spare terrarium as a frost cover, but now it looks to be entirely encased in ice:

The big box is icy too:

Most of the trees look like this, though, a mystery for now:


I caved and drug everything into the fish room. I unfortunately forgot about my olive and pineapple guava.

The pineapple guava seems to be ok. I just stuck it in an aquarium like you.

The olive sat out on a slab. Seems ok. We will see in 2 more nights. I may put it in the empty fish tank next to it. I thought it would be dead, I was afraid to look.


This was after 14 F, yes?

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14.7° was the lowest, which rounds up to 15 I guess, but yes it was after that worst night. I’m planning to go walk around again in a few minutes and I’ll update the guabiju thread with photos when I do that. It’s very possible at this point there’s damage that’s just not evident yet.


Just FYI in case anyone looks at that link and wonders about the sudden change in temperatures for Floater 2, I have moved it around to a few different trees in the last couple days, to see what kind of deltas you get for each type of protection. Fleece + ceramic heat lamp is the clear winner, no surprises there. I was a little surprised to see that an LED grow light (32W) under tattered fleece produces a similar overnight delta to a fully sealed up polycarbonate box with a string of incandescent string lights. Just a few degrees difference either way. The part indicated in red compares those two last night:


I moved the tree inside the first day that it got down to 17 degrees. I will see what parts survived in a few weeks, but the leaves and half the stem are definitely crisped


Based on data from a sensor, I realized we’d reached the point where the fleece was holding in the cold, so I just went around and removed everything other than the polycarbonate box, which cannot come out until the mound of wood chips around the base defrosts. Here is that, though, as best as it can be seen through the panels:

Mostly I was greeted with obvious death above ground. I suspect the few exceptions may just be cases of less-obvious death, but only time will tell.

First, Poncho, which was in a cozy heated fleece house that kept above freezing the entire time. A very happy tree:

Next up, one of the surprises is Northrup, which was in a drafty fleece tent with only a 32w LED lamp as company. The sensor showed it was only 5°F warmer than the outside, at best, so that would’ve been an awful lot of cold for a long time, with a low in the upper teens on a couple nights. It looks OK on most branches, but I fear BOTH rootstocks are dead (I had in-grafted a second one this summer because the original one was almost killed last winter):

I may need to try taking some scionwood soon when I can tell better which parts are least damaged. This is a promising variety but I need to get it on an equally promising set of roots.

Two Duke seedlings that were under unheated fleece look to be dead above ground, or at least nearly so, time will tell if a bit of the main trunks make it but they show clear stem discoloration that usually means death of that branch:

This Aravaipa seedling had a bit of the main trunk survive last winter, and it may pull off the same trick this year even though it was not even under fleece, just a plastic stool with a kitchen trash bag pulled over it:

The graft of Ganter looks entirely dead, above the graft at least. It was covered with an old litter box, unheated and drafty:

The clump that huddled near the west wall of my house under loose-fitting/drafty fleece looks better than some of the others, but still likely lots of death to be revealed in coming days/weeks as the trees abort damaged leaves and branches. The one right against the concrete wall might be OK, and the Mexicola Grande seedling in the ground in their midst may have some stem and leaves even that are relatively undamaged:

The probe showed the middle of those pots was about +5°F compared to outside, so still pretty cold!

A Mexicola seedling that died above ground last winter unprotected looks very dead, but maybe the roots will be OK again. It got a stool and trash bag just like the Aravaipa seedling shown earlier, and did not fair as well:

And finally, one possible surprise, a first-year Del Rio seedling that had only an unheated plastic 5-gal bucket over it looks like some of the stem might make it and perhaps even a few lower leaves. But it might just show more serious injury on a delay:


I got impatient waiting for the mound of wood chips to defrost around the polycarbonate box, so I got some tools and chipped it away. Pretty solid ice, but only the first 3-4 inches, below that it was unfrozen, which is a good sign for this tree’s roots.

The leaves look pretty dead, as do many of the thinnest stems, but also a few leaves look less dead (only “mostly dead” :wink:), and some stems look only mildly damaged, too. The low in the box was 19.0°F, with many, many hours below freezing. Here’s the chart for the inside temperatures in the box since Friday:

I’ve cracked it open for ventilation, but will probably leave the box up until the end of winter, to save myself the hassle of reassembling it if we get another bad freeze.

In other more cheerful news, the greenhouse trees all seem to be loaded with swelling flower buds.

Walter Hole:


Both grafts of Duke are a little further behind but with almost 3x the total biomass of any other grafted variety, it’s the one most likely to actually set fruit this year:


Went ahead and removed the polycarbonate box, but I’ll keep it assembled in a corner of the yard for now. I think it is 50/50 whether the branches mostly recover or whether the tree aborts the whole trunk and focuses growth on the undamaged secondary shoot at the base. There’s lots of damage to the cambium but there may be enough of a patchwork of living tissue to stitch it all back together.


My 11 year-old, walking past that tree after school today:
“That tree doesn’t look so great. I don’t think your box worked.”

“It probably would look even worse if I hadn’t done that.”

“I don’t see how it could look much worse than that.”